1. Field of the Invention
The present invention relates to a thrust bearing and a bearing device that receive an axial force of a crankshaft of an internal combustion engine.
2. Description of the Related Art
The crankshaft of an internal combustion engine is rotatably supported, at a journal portion thereof, in a cylinder block lower portion of the internal combustion engine via a main bearing that is configured by combining a pair of half bearings in a cylindrical shape.
One or both of a pair of half bearings are used in combination with a half thrust bearing that receives a force in the axial direction of the crankshaft. The half thrust bearing is placed on at least one of both end surfaces of the half bearings in the axial direction.
The half thrust bearing receives the force in the axial direction that occurs in the axial direction of the crankshaft. Namely, the half thrust bearings are disposed for the purpose of bearing the force in the axial direction that is inputted to the crankshaft when the crankshaft is connected with a transmission by a clutch, or the like.
On a slide surface side of a half thrust bearing, thrust reliefs are formed so that the thickness of a member becomes thinner toward circumferential end surfaces in the vicinity of both ends in the circumferential direction of the half thrust bearing. In general, in the thrust relief, the length from the end surface in the circumferential direction of the half thrust bearing to the slide surface, and the depth at the end surface in the circumferential direction are made constant irrespective of a position in the radial direction. The thrust relief is formed to absorb positional displacement of the end surfaces of a pair of half thrust bearings at the time of assembling the half thrust bearings in a split type bearing housing (see FIG. 10 of JP-A-H11-201145).
The crankshaft of an internal combustion engine is borne, at the journal portion thereof, in the cylinder block lower portion of the internal combustion engine via a main bearing formed by a pair of half bearings. Lubricating oil is fed into a lubricating oil groove that is formed along an inner circumferential surface of the main bearing through a through-hole in a wall of the main bearing from an oil gallery in a cylinder block wall. In this manner, the lubricating oil is supplied into the lubricating oil groove of the main bearing, and thereafter, is supplied to the half thrust bearing.
Incidentally, in recent years, oil pumps for supplying lubricating oil of internal combustion engines have been downsized, and therefore, the supply amount of the lubricating oil to the bearings has been decreased. Accordingly, the leakage amount of the lubricating oil from the end surfaces of the main bearings becomes decreased, and the supply amount of the lubricating oil to half thrust bearings has also tended to decrease. As a countermeasure against it, for example, the art of enhancing oil retainability for lubricating oil by forming fine grooves to be provided side by side on the slide surface of a half thrust bearing is proposed (see JP-A-2001-323928).